The KIRK® Type SKRU consists of an interlock, a solenoid, and an auxiliary switch. To release the key, a signal must be sent to the solenoid from an external source. The SKRU is available in our SD and HD series.


The auxiliary switch used is a quick-make, quick-break device, which operates when the interlock key is rotated. The solenoid is designed to permit removal of the interlock key in response to an external electric signal. Normally, the key is trapped in the SKRU and the solenoid is de-energized. For a more compact product please see our SKPM interlock.


Our SKRU can be manufactured with various mechanical and electrical options; the push button and/or the LED signal lamp are the most popular. The main body of the SKRU is constructed of brass while the optional cover plate is aluminum and optional housing is made from fiberglass reinforced polyester. All components are UL recognized.  


  • Mounting Options – unhoused, cover plate only, or housed. The photo above shows all options of the SKRU. The housed SKRU is available front or back panel mounted.

  •  Key Removable – energized or de-energized. Please specify. Key removable energized is by far the most common.

  •  Multi-Cylinder - up to 2 cylinders available. The two-cylinder SKRU can be keyed either of two ways, 1) both keys released together once the solenoid is energized or, 2) keyed so that one initiating key and the external signal to the solenoid are required to release a held key.

  •  LED Signal Lamp – indicates that the external electric signal has been sent to the solenoid.

  • Push Button – connected in series with the solenoid - the push button must be pressed to allow the external electric signal to energize the solenoid.

  • Solenoid Voltage – 24VAC,120VAC, 240VAC, 24VDC, 48VDC 125VDC, or 250VDC.

  • Auxiliary Switch – double pole/double throw (DP/DT) is standard. The DP/DT switch is UL recognized and rated 10A 250VAC or VDC, or 15A 125VAC or VDC. Four pole/double throw (4P/DT) is available.

  •  Stamp Key Interchange - specify an alphanumeric code to be stamped on the cylinder face and the key (e.g. A1, A2, B1, etc. - up to 5 characters).

  • Protective Covers - see SD or HD Series Data Sheet for Protective Covers (3.1) for details.

trapped key interlocks



trapped key interlocks


The Type SKPM is a single cylinder interlock similar to the standard, unhoused SKRU in function but is more compact and is ideal where space is limited. The SKPM is designed to permit removal of the interlock key in response to an electric signal. However, instead of utilizing a terminal block, the SKPM is arranged so customers’ leads are wired directly to the solenoid and auxiliary switches. The SKPM is designed so that the key is removable only when the solenoid is energized.


All components are UL recognized. Reference the wiring diagrams on our website as needed.



  • Solenoid Voltage – 120VAC, 24VDC, 48VDC, or 125VDC.

  • LED Signal Lamp – an LED signal lamp kit is available to be wired by the installer. Shipped loose.

  • Push Button – a push button kit is available to be wired by the installer. Shipped loose.  


Note: If both the LED signal lamp and push button are selected, a combination signal lamp and push button device will be furnished.



Electromechanical Interlocks - solenoid controlled interlocks

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